Transylv. Rev. Syst. Ecol. Res. 8, (2009), "The Wetlands Diversity" 161 FISH SPECIES DIVERSITY IN THE RIVERS OF THE NORTH-WEST BULGARIA Teodora TRICHKOVA *, Tihomir STEFANOV **, Milen VASSILEV * and Mladen ZIVKOV * * Bulgarian Academy of Sciences, Institute of Zoology, 1 Tsar Osvoboditel Blvd., Sofia 1000, Bulgaria, [email protected], [email protected] ** Bulgarian Academy of Sciences, National Museum of Natural History, 1 Tsar Osvoboditel Blvd., Sofia 1000, Bulgaria, [email protected] KEYWORDS: North-West Bulgaria, biodiversity, indigenous species, conservation. ABSTRACT The rivers in the North-West Bulgaria belong to the Danube Basin. At present, they are slightly affected by industrial pollution and, except for their lower reaches, they are not regulated. In 2005, the fish species diversity in five rivers (Voinishka, Vidbol, Archar, Tsibritsa and Ogosta) was monitored. A total of 27 fish species belonging to seven families were recorded. Of them, 24 species are indigenous to the ichthyofauna of the Danube Basin. Most frequently occurred the species L. cephalus, G. gobio, R. amarus and B. petenyi. The greatest species diversity was registered in the rivers Ogosta (24 species), Lom (17 species) and Vidbol (16 species), and the lowest - in the Voinishka River (five species). 11 of the fish species recorded are of high conservation concern in Bulgaria. The main threats to fish populations are regulation by weirs and dikes in the lower reaches, water pollution, excessive fishing and poaching, and construction of micro-hydropower stations along the river courses. ZUSAMMENFASSUNG: Die Fischfauna in den Flüssen Nord-West Bulgariens. Die Flüsse im Nordwesten Bulgariens gehören zum Einzugsgebiet der Donau. Gegenwärtig leiden sie unter einer leichten Verschmutzung und lediglich in den Unterläufen bestehen wasserbauliche Einrichtungen. Im Jahr 2005 wurde die Fischartenzusammensetzung in fünf Flüssen (Voinishka, Vidbol, Archar, Tsibritsa und Ogosta) untersucht. Insgesamt wurden 27 Fischarten aus sieben Familien festgestellt, von denen 24 im Einzugsgebiet der Donau heimisch sind. Am häufigsten waren die Arten L. cephalus, G. gobio, R. amarus and B. petenyi. Die größte Artenvielfalt wurde in den Flüssen Ogosta (24 Arten), Lom (17 Arten) und Vidbol (16 Arten) nachgewiesen, während die niedrigste im Fluss Voinishka (fünf Arten) festgestellt wurde. 11 der nachgewiesenen Arten haben einen hohen Schutzstatus und sind für Bulgarien von großem naturschutzfachlichem Interesse. Die Hauptgefahren für die Fischpopulationen stellen die Dämme und Staumauern in den Unterläufen der Flüsse dar, außerdem die Wasserverschmutzung und die Überfischung. Dazu kommen noch Schwarzfischerei und die Errichtung zahlreicher kleiner Wasserkraftwerke in den Flussläufen. REZUMAT: Diversitatea speciilor de peşti în râurile din nord-vestul Bulgariei. Râurile din nord-vestul Bulgariei aparţin bazinului hidrografic al Dunării. În prezent, acestea sunt afectate în mică măsură de poluare şi, cu excepţia sectoarelor inferioare, nu sunt regulate. În 2005, s-a monitorizat diversitatea speciilor de peşti din cinci râuri (Voinishka, Vidbol, Archar, Tsibritsa şi Ogosta). În total, s-au identificat 27 de specii de peşti, aparţinând 162 T. Trichkova et al. – Fish species diversity in the rivers of North-West Bulgaria (161 ~ 168) la şapte familii. Dintre acestea, 24 de specii aparţin ihtiofaunei indigene a bazinului dunărean. Cele mai frecvente specii au fost L. cephalus, G. gobio, R. amarus şi B. petenyi. Cea mai mare diversitate a speciilor de peşti a fost înregistrată în râurile Ogosta (24 specii), Lom (17 specii) şi Vidbol (16 specii), iar cea mai scăzută în râul Voinishka (cinci specii). 11 dintre speciile de peşti înregistrate sunt strict protejate, în Bulgaria. Principalele ameninţări cu care se confruntă populaţiile de peşti sunt regularizările râurilor cu stăvilare şi baraje, în zona inferioară, poluarea apei, pescuitul excesiv şi braconajul, precum şi construcţia de microcentrale hidroelectrice de-a lungul cursurilor râurilor. INTRODUCTION The North-West Bulgaria and especially the West Balkan Mountains included in this region are known due to their high conservation priority. Two reserves - the Chuprene Biosphere Reserve and the Gornata Koriya Strict Nature Reserve, as well as 17 protected areas of national and international importance have been declared (Executive Environment Agency, Ministry of Environment and Water of Bulgaria). A proposal for designating the West Stara Planina Mountains as a nature park was made and the procedure has been under way (Vassilev et al., 1999). The status of the region and the development of the Bulgarian Natura 2000 network of protected areas necessitated having a complete knowledge about the fish species diversity in the rivers of the region. There are few studies on the ichthyofauna of the North-West Bulgarian rivers. Drensky (1951) reported on the occurrence of some fish species. Michailova (1970) studied the ichthyofauna in the rivers of the West Stara Planina Mountains in 1963 - 1964. Summary information about the ichthyofauna of the Danube tributaries was published by Karapetkova (1994), Karapetkova and Zivkov (1995) and Karapetkova et al. (1998). Some unpublished and newly obtained data about the species diversity of the ichthyofauna in the West Balkan Mountains for the period 1985 - 1999 were summarized by Trichkova et al. (2004). The goal of the present study was to make an ichthyological inventory of the rivers in the North-West Bulgaria in terms of species composition and conservation status. MATERIAL AND METHODS The study area comprises a territory of 9,105.38 km2, which is approximately 8% of the territory of Bulgaria. It is characterized with a diverse landscapes and geographic conditions. The area is constructed of three structural entities - the Danube Plain, transitional “Predbalkan” and the Stara Planina Mountains, the latter two known as the Balkan Mountains. The variation in elevation is over 1,800 m. The area includes 13 main river catchments affiliated to the Danube River drainage basin. At present, the rivers are slightly affected by industrial pollution, and except for their lower reaches, they are not regulated. Their water is used mainly for irrigation and less for production of electricity. The water chemical characteristics of the rivers for the period 2000 - 2006 (mean values) were the following: water temperature in the range of 9.1 - 15.6oC (10.7 - 22.2oC for April-September period); pH range of 7.8 - 8.4; electro conductivity of 100 - 744 μS/cm; dissolved oxygen of 7.3 - 9.8 mg/l; dissolved solids of 66.7-496.3 mg/l; suspended solids of 17.8 - 68.1 mg/l; and Ca concentration range of 16 - 94 mg/l (Executive Environment Agency, Ministry of Environment and Water of Bulgaria). In April-September 2005, the fish species diversity in five river basins: Voinishka, Vidbol, Archar, Tsibritsa and Ogosta (Tab. 1) was monitored. Totally, 40 sites along the entire reaches of the rivers except the uppermost reaches and estuaries, as well as some tributaries were sampled (Tab. 1). Sampling was made by electrofishing and beach seine. Transylv. Rev. Syst. Ecol. Res. 8, (2009), "The Wetlands Diversity" 163 Table 1: River lengths and catchment areas, location of sampling sites, North-West Bulgaria. Length Catchment Sites - Location, Coordinates River (km) Area (ha) (Latitude N, Longitude E, degrees), Altitude (m, a.s.l.) (1) Bukovets, 43°55'42''N, 22°45'34''E, 58 m a.s.l. Voinishka 60 27,700 (2) 5 km upstream the river mouth, 43°55'13''N, 22°49'32''E, 46 m a.s.l. (3) Valchek, 43°46'53''N, 22°4313E, 148 m a.s.l. (4) Stratsimirovo 43°49'36''N, 22°44'12''E, 106 m a.s.l. (5) Bozhuritsa 43°53'34''N, 02°45'00''E, 81 m a.s.l. Vidbol 62 33,000 (6) Dunavtsi, 2 km upstream (7) Dunavtsi, the bridge 43°54'11'N, 22°48'21''E, 44 m a.s.l. (8) Dunavtsi, downstream (9) Dimovo, upstream 43°44'06''N, 22°43'05''E, 134 m a.s.l. (10) Dimovo, the bridge 43°44'18''N, 22°43'30''E, 134 m a.s.l. Archar 59 36,500 (11) Darzhanitsa 43°48'37''N, 22°5055E, 66 m a.s.l. (12) Archar, upstream (13) Archar, the old bridge 43°48'45''N, 22°55'08''E, 48 m a.s.l. (14) Borovitsa (15) Ruzhintsi, upstream (16) Roglets 43°40'33''N, 22°55'61''E, 144 m a.s.l. Lom 93 114,000 (17) Dabova Machala (18) Staliiska Machala 43°43'19''N, 23°09'36''E, 44 m a.s.l. (19) Lom Town 43°48'30''N, 23°14'39''E, 38 m a.s.l. (20) Klisuritsa (21) Slavotin 43°33'46''N, 23°04'00''E, 198 m a.s.l. (22) Between Slavotin and Doctor Yosifovo 43°32'08''N, 23°06'26''E, 191 m a.s.l. (23) Bezdenitsa, the bridge Tsibritsa 88 93,400 (24) Dolno Tserovene (25) Dalgodeltsi (26) Yakimovo (27) Valchedram 43°41'33''N, 23°27'06''E, 64 m a.s.l. (28) Zlatiya 43°44'58''N, 23°29'16''E, 39 m a.s.l. (29) Dolen Tsibar, upstream 43°47'51''N, 23°30'06''E, 41 m a.s.l. (30) Gavril Genovo (31) Montana Town 43°24'07''N, 23°13'52''E, 149 m a.s.l. (32) Michailovo Ogosta 144 315400 (33) Hairedin (34) Miziya, upstream confluence with Skat River 43°41'30''N, 23°49'35''E Shugavitsa, (35) Sumer, 43°20'46''N, 23°19'36''E, 189 m a.s.l. Ogosta basin (36) Tarnava 43°30'24''N, 23°53'08''E, 106 m a.s.l. (37) Altimir 43°31'39''N, 23°48'51''E, 79 m a.s.l. Skat, (38) Galiche 43°33'38''N, 23°51'44''E, 64 m a.s.l. Ogosta (39) Miziya, upstream 43°40'13''N, 23°51'26''E, 49 m a.s.l.